feat: add phase 1 runnable skeleton

apps/companion/src/index.ts

@@ -0,0 +1,13 @@
+import { buildApp } from './app.js';
+
+const port = Number.parseInt(process.env.PORT ?? '8787', 10);
+const host = process.env.HOST ?? '0.0.0.0';
+
+const app = await buildApp();
+
+try {
+  await app.listen({ port, host });
+} catch (error) {
+  app.log.error(error);
+  process.exit(1);
+}